The present invention relates to a linear motor, and more particularly to a linear motor operated as a two-phase and a multi-phase linear pulse motor or a brushless DC linear motor.
FIG. 10 is a longitudinal sectional view illustrating a permanent magnet type cylindrical linear motor pertinent to the present invention.
In FIG. 10, a stator core 101 of a stator 100 of the permanent magnet type cylindrical linear motor includes a ring-like yoke portion having a small inner diameter and forming ring-like stator tooth tops 102a and a ring-like yoke portion having a large inner diameter and forming ring-like stator tooth bottoms 102b, both the yoke portions being laminated alternately in the shaft direction. Thus, stator teeth 102 composed of a number of ring-like tooth tops 102a and ring-like tooth bottoms (grooves) 102b are formed in the inner peripheral surface of the stator core 101 at equal pitches in the shaft direction.
Ring-like windings 103, 104, . . . 110 are disposed in the ring-like tooth bottoms (grooves) 102b, respectively. The ring-like windings 103, 104, . . . 110 are configured to have two phases in total as shown in FIG. 11 so that the ring-like windings 103, 105, 107 and 109 are connected so that the polarities thereof are reversed alternately to form one phase (A phase) and the ring-like windings 104, 106, 108 and 110 are connected so that the polarities thereof are reversed alternately to form the other phase (B phase). Since the stator 100 is configured as above, the pole pitch of the stator 100 is four times the tooth pitch of the stator teeth 102.
Further, a mover core 301 of a mover 300 is cylindrical and permanent magnet poles 302 magnetized to have the polarities different radially and alternately are disposed on the outer periphery of the mover core at a pitch equal to twice the tooth pitch of the stator teeth 102. Consequently, the pole pitch of the mover 300 is four times the pitch of the stator teeth and is coincident with the pole pitch of the stator 100.
The two-phase windings disposed in the stator core 101 are shifted from each other by the tooth pitch of the stator teeth, that is, a quarter of the pole pitch of the stator in the shaft direction, and the linear motor constitutes a two-phase permanent magnet type cylindrical linear pulse motor having a basic amount of movement for each step which is equal to a quarter of the pole pitch, that is, the pitch of the stator teeth.
In the permanent magnet type cylindrical linear pulse motor as configured above, however, in order to connect the ring-like windings 103, 104, . . . 110, it is necessary to provide notches in the outer peripheral portion of the ring-like yoke portions of the tooth tops 102a and the tooth bottoms 102b and pull out ends of the windings 103, 104, . . . 110 from the notches so that the pulled-out ends are connected and are accommodated in lead pulling-out grooves formed in the notches. Accordingly, there is a problem that the operation efficiency of the motor assembly is deteriorated.
On the other hand, the size of the tooth bottoms 102b of the stator teeth 102 accommodating the windings 103, 104, . . . 110 depends on the pitch of the stator teeth. When the pitch of the stator teeth is small, the tooth bottom 102b cannot be made larger and the ampere-conductors per phase cannot be increased. Accordingly, there is a problem that the driving force is low.
Further, since the motor is of the permanent magnet type, the motor can be operated as a brushless DC motor theoretically, while there is a problem that it is necessary to provide sensor means for detecting the position of the mover separately for that purpose.